The invention relates to a floating wind turbine comprising a floating foundation, a tower arranged on the floating foundation, and an energy conversion unit which is mounted on the tower and comprises a rotor, the wind turbine being designed as a downwind turbine, the floating foundation being rotatable anchored, and the tower being rotationally fixedly connected to the floating foundation on the one hand and the energy conversion unit on the other hand.
Floating wind turbines for large water depths are for example known from EP 2 271 547 B1. Such structures consists in particular from a frame that is designed in the shape of an isosceles triangle in a top view, at whose apexes the columns are arranged, the tower of the wind turbine being erected on one of these columns or, supported centrally by a bearing structure, between the columns.
However, a disadvantage of this design is the complexity of the construction and the high labour expenditure for manufacturing the frame. The known installation in particular requires a relatively large horizontal and vertical extent for taking up the forces occurring at the rotor of the wind turbine, and therefore depends both for the construction and also for the installation on great water depths.
The German patent application No. 10 2014 102 481.8 previously filed by the applicant already describes a floating wind turbine having the features mentions initially, that exhibits a foundation arranged below the water line and formed from a plurality of buoyancy bodies, the foundation basically having to be regarded as an extension of the tower of the wind turbine. There it is particularly provided that the tower of the wind turbine that is designed as a downwind turbine is rotationally fixedly connected to the foundation on the one hand and to the energy conversion on the other hand and the floating foundation is rotationally anchored and the tower exhibits, at least in sections, a profile that supports wind direction tracking. Even though the system is designed for use in deep waters having depths >200 m, since for vertically stabilizing the system a relatively long section, formed by the foundation, is required under water. However, the onshore manufacture of the system requires less space than for the system initially mentioned.
EP 1 269 018 B1 finally discloses a wind turbine that exhibits, as the foundation, a catamaran-like buoyancy body and is particularly suitable for installation in shallow waters. This system is designed as a downwind turbine, where likewise a yaw bearing having a yaw drive being dispensed with as a result of the fixed connection from tower to foundation on the one hand and tower to the energy conversion unit on the other hand and it instead being provided that the system, by means of chains or ropes, is anchored to an anchoring point rotatable about the latter, so that the system automatically aligns itself according to the prevailing wind direction.
In the wind direction, the tower exhibits an aerodynamic profile for minimizing the lee side and exhibits in particular a stiffening element that runs from the upper tower area upwind, for example designed as a rope, that is connected to the foundation.
However, the disadvantage here is the catamaran-like design of the foundation and the arrangement of the tower on a web connecting the buoyancy bodies, so that the loads occurring at the rotor and/or at the energy conversion unit are dissipated into the foundation in a rather one-sided manner and the floating wind turbine tends to list.
In addition to the construction of offshore wind turbines themselves, it is also their installation that represents a particular challenge. A high degree of completion is in principle desirable onshore, so that the offshore installation can take place with relatively low effort and during a short period of time. In this manner the offshore wind turbine known from the previously mentioned EP 2 271 547 B1 is completely produced onshore and towed to the location of its use where it is anchored on the sea bed by means of a plurality of anchor chains.
The disadvantage of this anchoring is, however, the high effort for decoupling the mooring lines that anchor the offshore wind turbine and also the electrical connection to the submarine cable so that in the case of maintenance or repair, if the system is to be towed again into the harbour, long downtimes have to be expected despite assumed favourable weather conditions.